Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$38.57	9.859%	$42.3726	$42.37	$42.35	$42.40
Purchase #2	$10.84	7.162%	$11.6164	$11.62	$11.60	$11.60
Purchase #3	$156.78	11.294%	$174.4867	$174.49	$174.50	$174.50
Purchase #4	$126.41	8.225%	$136.8072	$136.81	$136.80	$136.80
Purchase #5	$108.51	7.404%	$116.5441	$116.54	$116.55	$116.50
Purchase #6	$115.44	6.639%	$123.1041	$123.10	$123.10	$123.10
Purchase #7	$16.88	10.224%	$18.6058	$18.61	$18.60	$18.60
7 purchase totals =	$573.43		$623.5369	$623.54	$623.50	$623.50